As the performance and fuel consumption of hydraulic machines have recently been more and more improved to save energy, there has been increasingly higher demand of providing higher sealability and lower friction to oil seal rings used in rotary shafts and reciprocating parts of the hydraulic machines. Conventionally used for the oil seal rings are metals or plastics from the viewpoint of resistance to sliding heat, hydraulic pressure, oil, etc. Examples of metals used for the oil seal rings include cast iron such as FC25, etc. There are only a few examples of plastics having sufficient heat resistance and slidability, and commercially available resins that are usable for the oil seal rings are only polyetheretherketone resins (PEEK resins), tetrafluoroethylene resins (PTFE resins), polyimide resins (PI resins) or polyphenylene sulfide resins (PPS resins).
Al or Al alloys are widely used for to reduce the weight of automatic transmissions, and when these metals are used for sliding mates, on which oil seal rings slide, the oil seal rings are generally made of cast iron or PTFE resins. However, the oil seal rings made of cast iron are poor in sealability though they have excellent wear resistance. In contrast, the oil seal rings made of the PTFE resins are excellent in sealability, though they are extremely poor in wear resistance, resulting in abnormal wear of Al or its alloys in a short time.
Under such circumstances, various proposals have been made to provide sliding members excellent in wear resistance and sealability. For example, JP 55-7848 A discloses that carbon fibers and solid lubricant particles are added to a polyphenylene sulfide resin, to obtain a sliding member excellent slidability with soft (relatively low-hardness), non-ferrous metals such as Al alloys. Because the PPS resin is as good as the PTFE resin in heat resistance and the next to the PTFE resin in chemical resistance, it is suitable for the oil seal members. However, the oil seal member made only of the PPS resin is insufficient in wear resistance and slidability. Therefore, reinforcement by carbon fibers and lubrication by solid lubricant particles are given to the PPS resin, so that the PPS resin can be used for the oil seal members.
However, the above conventional, PPS resin-based sliding member is disadvantageous in poor adhesiveness between fibrous fillers such as carbon fibers and the PPS resin. Thus, the fibrous fillers are likely pulled out from a sliding surface of the member during a sliding operation, causing the plastic flow of the PPS resin. Further, the pulled-out fibrous fillers cause abrasive wearing, thereby accelerating the wear of the sliding mate. Furthermore, the oil seal ring is so difficult in assembling because of brittleness peculiar to the PPS resin, that it cannot be put into practical use without difficulty.